Multi-operational valve

ABSTRACT

A valve for selectively fluidly communicating a first fluid volume and a second fluid volume includes a valve body, an inlet orifice in fluid communication with the first fluid volume, and an outlet aperture in fluid communication with the second fluid volume. The valve also includes an activation member axially movable relative to the valve body. The valve is operable in a first mode in which the valve opens in response to manual actuation of the activation member. The valve is operable in a second mode in which the valve opens when a pressure difference between the first and second fluid volumes reaches a predetermined value, and the valve closes when the pressure difference between the first and second fluid volumes is less than the predetermined value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/792,356 filed on Mar. 15, 2013, and to U.S. Provisional PatentApplication No. 61/677,554 filed on Jul. 31, 2012, the entire contentsof both of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to fluid valves and, more particularly, toa valve that has multiple modes of operation.

BACKGROUND OF THE INVENTION

Hydraulic systems require the use of valves to regulate, direct, and/orcontrol the flow of fluid throughout the system. In power tools or otherhydraulically driven systems, valves are used to direct the flow offluid to do work, such as by moving a piston within a cylinder orcharging a set of actuators. Depending on the desired flow properties,different types of valves are used, each having its own set of abilitiesand drawbacks.

SUMMARY OF THE INVENTION

The present invention provides, in one aspect, a valve for selectivelyfluidly communicating a first fluid volume and a second fluid volume.The valve includes a valve body, an inlet orifice in fluid communicationwith the first fluid volume, and an outlet aperture in fluidcommunication with the second fluid volume. The valve also includes anactivation member axially movable relative to the valve body. The valveis operable in a first mode in which the valve opens in response tomanual actuation of the activation member. The valve is operable in asecond mode in which the valve opens when a pressure difference betweenthe first and second fluid volumes reaches a predetermined value, andthe valve closes when the pressure difference between the first andsecond fluid volumes is less than the predetermined value.

Other features and aspects of the invention will become apparent byconsideration of the following detailed description and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a valve according to one construction of theinvention in a closed configuration.

FIG. 2 illustrates the valve of FIG. 1 in an intermediate stage of amanually opened configuration.

FIG. 3 illustrates the valve of FIG. 1 in a manually openedconfiguration.

FIG. 4 illustrates the valve of FIG. 1 in an automatically openedconfiguration.

FIGS. 5 and 6 illustrate another hydraulic system containing the valveof FIG. 1.

FIG. 7 illustrates a valve according to another construction of theinvention in a closed configuration.

FIG. 8 illustrates the valve of FIG. 7 in an open configuration.

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, it is to be understood thatthe phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting.

DETAILED DESCRIPTION

FIGS. 1-4 illustrate a hydraulic system 10 having a first fluid volume14 under a first pressure and a second fluid volume 18 under a secondpressure, which is lower than the first pressure. The hydraulic system10 also includes a valve 22 for controlling the flow of fluid betweenthe first fluid volume 14 and the second fluid volume 18. In someconstructions, the second fluid volume 18 may include a reservoir.

Although not illustrated, the first fluid volume 14, the second fluidvolume 18, or a combination thereof can be utilized in industrialsettings to do work. Some examples may include activating a piston,driving a crimping head, driving a cutting head, driving a press, andthe like.

Illustrated in FIGS. 1-4, the valve 22 includes a body 26, a firstplunger 30, a second plunger 34, an activation rod 38 coupled to thefirst plunger 30, and a pointed tip 42 located at a distal portion 114of the second plunger 34. Alternatively, the valve 22 can include acheck ball located at the distal portion 114 of the second plunger 34.During operation, the valve 22 is operable in both a manual mode and anautomatic mode. During the manual mode (e.g., the valve 22 is openedmanually by the user), the valve 22 remains in an open configuration(e.g., allowing fluid to flow from the first fluid volume 14 to thesecond fluid volume 18) until the pressure of the first fluid volume 14is substantially equal to the pressure of the second fluid volume 18. Incontrast, when the valve 22 is in the automatic mode (e.g., the valve 22is opened automatically by pressure acting on the pointed tip 42), thevalve 22 opens when the pressure difference between the first fluidvolume 14 and the second fluid volume 18 exceeds a predetermined value(e.g., 7,600 psi) and closes when the pressure difference drops belowsaid value.

The body 26 of the valve 22 is substantially cylindrical in shape havinga base 46 and an annular wall 50 extending axially from the base 46. Inthe illustrated construction, the valve 22 includes an end cap 52coupled to the base 46 and defining an input or inlet aperture 54 influid communication with the first fluid volume 14. In otherconstructions, the end cap 52 can be integrally formed with the base 46.Furthermore, the annular wall 50 defines an output or outlet aperture 58in fluid communication with the second fluid volume 18. The end cap 52also includes an orifice or seat 62, proximate the input aperture 54, toact as a seat for the pointed tip 42 of the second plunger 34.

The first plunger 30 of the valve 22 is substantially disk shaped andincludes a central aperture 66. The first plunger 30 also defines anannular groove 70 about its perimeter. During operation, the plunger 30moves axially within the body 26 between a first position (FIG. 1),where the plunger 30 is positioned proximate the end cap 52, and asecond position (FIG. 3), where the plunger 30 is positioned a distancefrom the end cap 52. More specifically, when the first plunger 30 is inthe first position, a bottom 74 of the plunger 30 is positioned betweenthe end cap 52 and the output aperture 58, at least partially blockingthe aperture 58. Furthermore, when the plunger 30 is in the secondposition, the bottom 74 is above the output aperture 58 leaving theaperture 58 unblocked. In the illustrated construction, the plunger 30is biased towards the first position by a first spring 78. The firstplunger 30 also includes a flow control aperture 82 extending betweenthe bottom 74 and the annular groove 70.

The first plunger 30 also includes a cylindrical wall 86 extendingaxially therefrom and co-axial with the central aperture 66. Whenassembled, the cylindrical wall 86 at least partially contains thesecond plunger 34 therein. The cylindrical wall 86 also acts as aconnecting point between the first plunger 30 and the activation rod 38(described below).

The activation rod 38 is coupled to the first plunger 30 and movesaxially therewith. The activation rod 38 includes a distal end (notshown) where the user can manually interact with the valve 22. Duringoperation, the user manually alters the position of the rod 38 withrespect to the body 26, causing the first plunger 30 to move between thefirst and second positions. The activation rod 38 also includes a bottomsurface 90 that, when assembled, interacts with the second plunger 34.

The second plunger 34 includes a body 94 having a generallyfrustoconical contact surface 98 from which the distal portion 114 ofthe plunger 34 extends. In other constructions, the second plunger 34can be generally T-shaped, such that the distal portion 114 of theplunger extends generally perpendicular to the contact surface 98.During operation, the second plunger 34 is moveable with respect to thefirst plunger 30 between a sealed position (FIGS. 2 and 3), where thecontact surface 98 forms a seal with the central aperture 66 of thefirst plunger 30, and an unsealed position (FIGS. 1 and 4), where thecontact surface 98 is spaced a distance from the first plunger 30 toallow fluid to flow through the central aperture 66. In the illustratedconstruction, the second plunger 34 is biased towards the sealedposition by a second spring 106.

The distal portion 114 of the second plunger 34 has an outer diametersmaller than a diameter of the central aperture 66. As such, when thevalve 22 is assembled, the distal portion 114 of the plunger 34 extendsthrough the central aperture 66 creating a gap 110 therebetween. Whenthe valve 22 is closed, the pointed tip 42 of the distal portion 114 isin engagement with the seat 62 of the end cap 52 to form a sealtherewith. In alternate constructions, the distal portion 114 can bearagainst a check ball or other element to form a seal with the seat 62 ofthe end cap 52.

The body 94 of the second plunger 34 includes a flange 118 extendingaxially therefrom proximate the contact surface 98. The flange 118includes an outer diameter less than the inner diameter of thecylindrical wall 86 to define a gap 122 between the flange 118 and thecylindrical wall 86. In some constructions, the flange 118 can include anotch formed therein and extending axially inwardly to facilitate fluidflow past the flange 118 when the second plunger 34 is in the unsealedposition. In the illustrated construction, the cross-sectional area ofthe gap 122 is greater than the cross-sectional area of the gap 110between the distal portion 114 and the central aperture 66 to facilitatefluid flow past the flange 118 when the second plunger 34 is in theunsealed position. In other constructions, the cross-sectional area ofthe gap 122 may be less than or equal to the cross-sectional area of thegap 110.

During operation, the valve 22 generally remains in the closedconfiguration (FIG. 1) where no fluid can flow between the firsthydraulic volume 14 and the second hydraulic volume 18. When the valve22 is in the closed configuration, the first spring 78 biases the firstplunger 30 into the first position while the second spring 106 biasesthe second plunger 34 towards the input aperture 54 such that thepointed tip 42 is biased into engagement with the seat 62, therebysealing the input aperture 54 from the first hydraulic volume 14.

To operate the valve 22 in the manual mode, the user manually actuatesthe activation rod 38 in a first direction A, thereby causing the firstplunger 30 to move towards the second position and away from the end cap52. As the first plunger 30 travels, the pointed tip 42 of the secondplunger 34 remains in contact with seat 62, maintaining the seal by wayof the biasing force produced by the second spring 106. Morespecifically, the force produced by the second spring 106 must be greatenough to overcome the force acting on the small area of the tip 42 bythe first fluid volume 14. As such, the second plunger 34 remainsstationary as the first plunger 30 begins to move.

The first plunger 30 continues to move axially with the activation rod38 until the contact surface 98 of the second plunger 34 contacts thefirst plunger 30 (FIG. 2). Once this occurs, the second plunger 34beings moving axially with the first plunger 30 away from the end cap 52and the force from the second spring 106 maintains the seal between thecontact surface 98 and the central aperture 66 of the first plunger 30.

The user continues to move the activation rod 38 in direction A untilthe first plunger 30 reaches the second position and the tip 42 of thesecond plunger 34 disengages from the seat 62 allowing fluid from thefirst fluid volume 14 to flow into the valve 22 through the inputaperture 54. Since the central aperture 66 is sealed by the contactsurface 98 of the second plunger 34, all the fluid entering the valve 22flows along path M (FIG. 3), and exits through the output aperture 58formed in the body 26. Once the valve 22 has been opened in manual mode,the valve 22 will remain in the open configuration (FIG. 3) due to thefluid pressure acting on the bottom surface 74 of the first plunger 30,which has a much greater surface area than the tip 42. The valve 22remains open until the pressure difference between the first fluidvolume 14 and the second fluid volume 18 has nearly reached zero.

As the pressure difference between the first fluid volume 14 and thesecond fluid volume 18 reduces, the first spring 78 begins to move thefirst plunger 30 towards the first position. Once the pressuredifference has decreased to a given level (e.g., nearly zero), the firstplunger 30 will have moved to where it will begin to cover or block theoutput aperture 58 (FIG. 2). At this time, the aperture 58 becomesaligned with annular groove 70, forcing the working fluid to flowthrough the flow control aperture 82 formed in first plunger 30. Sincethe area of the flow control aperture 82 is smaller than the area of theoutput aperture 58, the speed the fluid able to travel through the valve22 is reduced.

The reduced fluid movement continues until the pressure differencebetween the first fluid volume 14 and the second fluid volume 18 hasbeen substantially eliminated and the tip 42 is re-seated, returning thevalve 22 to the closed configuration, described above (FIG. 1).

To operate the valve 22 in the automatic mode, the pressure differencebetween the first fluid volume 14 and the second fluid volume 18 mustexceed a predetermined value (e.g., 7,600 psi). Once the pressuredifference has exceeded the predetermined value, hydraulic pressureacting on the small surface area of the tip 42 through the inputaperture 54 is great enough to cause the tip 42 to automatically unseat(FIG. 4). The second plunger 34 acts on the bottom surface 90 of theactivation rod 38, forcing the first plunger 30 and the activation rod38 to move together in the direction of arrow A, against the biasingforce of the first spring 78. Fluid from the first fluid volume 14 isthen allowed to flow into the valve 22 through the input aperture 54.

With continued reference to FIG. 4, since the initial force for openingthe valve 22 is exerted on the distal portion 114 of the second plunger34 instead of on the activation rod 38 as described above, the secondplunger 34 is in the unsealed position when the pointed tip 42 isunseated by the fluid pressure. As such, fluid flows along path Uthrough the central aperture 66 to the second fluid volume 18. Becausethe fluid at least partially bypasses the output aperture 58 and thefirst plunger 30, there is not enough pressure exerted on the bottom 74of the first plunger 30 to overcome the first spring 78 and hold thevalve 22 open. Therefore, the valve 22 immediately re-closes once thepressure differential between the first fluid volume 14 and the secondfluid volume 18 drops below the predetermined value that is required tounseat the pointed tip 42. Stated differently, since the fluid is ableto bypass the first plunger 30 (e.g., through the central aperture 66),the valve 22 is not held open by fluid pressure acting on the relativelylarge surface area of the bottom 74 of the first plunger 30 (as is thecase in the manual mode).

Once the pressure differential between the first fluid volume 14 and thesecond fluid volume 18 has dropped below the predetermined value, theforces from the first and second springs 78, 106 bias the first andsecond plungers 30, 34 towards the end cap 52. This in turn causes thepointed tip 42 of the second plunger 34 to engage the seat 62. The valve22 then returns to the closed configuration as described above (FIG. 1).

The relative sizes of the first plunger 30, the second plunger 34, andthe tip 42 along with the relative strengths of the first spring 78 andthe second spring 106 can be altered to customize the operation of thevalve 22. More specifically, the above attributes are altered todetermine the predetermined pressure difference needed to automaticallyopen the valve 22, the pressure at which the valve 22 will re-close inmanual mode, and the like. For example, in the illustrated construction,the first spring 78 is sufficiently strong to overcome the fluidpressure acting on the small surface area of the tip 42 as pressurebuilds within the first hydraulic volume 14 (up to the predeterminedvalue). However, the first spring 78 is also sufficiently weak to allowfluid pressure acting on the larger surface area of the bottom 74 of thefirst plunger 30 hold the valve 22 open once the tip 42 has beenmanually unseated.

FIGS. 5 and 6 illustrate another construction of a hydraulic system 500pertaining to a hand held hydraulic tool containing the valve 22described above. The hydraulic system 500 includes a working piston 504moveable within a cylinder 508 between a rest position (FIG. 5) and anactuated position (FIG. 6). The hydraulic system 500 also includes areturn spring 512 biasing the piston 504 towards the rest position.

In the illustrated construction, the first fluid volume 14 is in fluidcommunication with the working volume 516 of the device. Duringoperation, a pump 506 draws fluid from a reservoir 520 (e.g., the secondfluid volume 18) and pumps fluid, under pressure, into the workingvolume 516 to bias the working piston 504 towards the actuated position.

Once the piston 504 is in the actuated position, the user may return thepiston 504 to the rest position by manually biasing the activating rod38 and placing the valve 22 in the manual operation mode. Once manuallyopened, the valve 22 allows fluid to flow from the working volume 516and into the reservoir 520 (e.g., the fluid flows from the first fluidvolume 14 to the second fluid volume 18).

As fluid leaves the work volume 516, the return spring 512 is able tobias the piston 504 toward the rest position. As the piston moves towardthe rest position, the pressure of the fluid within the first fluidvolume 14 is created by the energy stored within the return spring 512.Therefore, as the piston 504 continues to move toward the rest position,energy is released from the return spring 512 causing the pressure ofthe fluid in the first fluid volume 14 to drop. As the pressure of thefirst fluid volume 14 drops, the pressure differential between the firstfluid volume 14 and the second fluid volume 18 approaches zero.

Once the pressure within the first fluid volume 14 has decreased to agiven level, the first plunger 30 will begin to cover or block theoutput aperture 58. At this time, the aperture 58 becomes aligned withannular groove 70 forcing the working fluid to flow through the flowcontrol aperture 82 formed in the bottom of the first plunger 30. Sincethe area of the flow control aperture 82 is smaller than the area of theoutput aperture 58, the speed the fluid able to leave the work volume516 is reduced and the speed of the piston 504 returning to the restposition is slowed. This feature also allows the piston 504 to morefully return to the rest position since movement within the cylinder 508is still permitted until the pointed tip 42 is fully seated.

The reduced speed movement of the piston 504 continues until the piston504 has successfully returned to the rest position, at which time thevalve 22 will return to the closed configuration, as described above.

In instances where operating pressures within the work volume 516 exceedthe pressure within the reservoir 520 beyond the predetermined value(e.g., if the piston 504 becomes jammed or the user attempts to cutmaterial beyond the specifications of the device) the valve 22 willenter the automatic operation mode. During this mode, the valve 22 willopen, as described above, to allow fluid in the work volume 516 to flowinto the reservoir 520 until the pressure difference between work volume516 and the reservoir 520 falls below the predetermined value. Once thepressure differential is low enough, the valve 22 will close asdescribed above.

Therefore, the piston 504 will only travel a short distance within thecylinder 508, less than the total distance between the actuated positionand the rest position. Note the piston 504 will not automatically returnall the way to the rest position as was the case during the manualactuation of the valve 22.

Although the construction illustrated in FIGS. 5 and 6 is shown drivinga piston within a cylinder, in other constructions the valve 22 can beinstalled in alternate, portable hydraulic power tools such as powercrimpers and hydraulic press tools.

FIGS. 7 and 8 illustrate another construction of a hydraulic system 600pertaining to a hand held hydraulic tool and containing a valve 602according to another construction of the invention. The hydraulic system600 includes a working piston or ram 604 moveable within a cylindricalram chamber 608 between a rest position and an actuated position. Theram 604 is operably coupled to a working element (not shown), such as acrimping head, a cutting head, a press, and the like. The hydraulicsystem 600 also includes a return spring 612 biasing the ram 604 towardsthe rest position.

In the illustrated construction, the ram 604 includes a disk-shapedsealing member 614 that creates a substantially fluid-tight seal withthe ram chamber 608. The sealing member 614 defines a working volume616, disposed between the sealing member 614 and a proximal wall 618 ofthe ram chamber 608. During operation, a pump 606 draws fluid from areservoir 620 and pumps fluid, under pressure, through a supply passage622 and into the working volume 616 to bias the ram 604 towards theactuated position.

The valve 602 includes a valve stem 632 having a poppet 636 located at adistal end of the valve stem 632, and a valve seat 640 having a passage644 extending through the valve seat 640. The passage 644 is in fluidcommunication with the supply passage 622 and working volume 616 of theram chamber 608. The poppet 636 includes a pointed tip 652 configured tosubstantially seal the passage 644 when the valve 602 is in a closedconfiguration (FIG. 7).

The valve stem 632 is axially moveable to define the closedconfiguration (FIG. 7) and an open configuration (FIG. 8) of the valve602. The valve stem 632 is biased towards the closed configuration by aspring 656 (best illustrated in FIG. 8). As the ram 604 moves from therest position toward the actuated position, against the biasing force ofthe return spring 612 and against any load applied to the workingelement, fluid pressure builds within the working volume 616. This fluidpressure also pushes against the tip 652 of the poppet 636, against thebiasing force of the spring 656. In the illustrated construction, thevalve 602 functions as a manual-release valve and includes an actuator(not shown) operable by the user to move the valve 602 toward the openconfiguration. Since the area of the tip 652 exposed to the fluidpressure of the working volume 616 is relatively small, during normaloperation of the hydraulic system 600, the valve 602 remains in theclosed configuration until actuated by the user.

As the user operates the actuator, the valve 602 moves toward the openconfiguration. The seal between the tip 652 and the passage is broken,and fluid from the working volume 616 flows into a valve chamber 660defined between the valve seat 640 and the poppet 636. The fluid flowinginto the valve chamber 660 presses against the face of the poppet 636,and the fluid is able to overcome the biasing force of the spring 656because the surface area of the poppet 636 is much greater than thesurface area of the tip 652. Therefore, once the valve 602 is opened bythe user, the fluid pressure acting on the poppet 636 causes the valve602 to remain in the open configuration without requiring additionalinput from the user.

The valve 602 includes an orifice 664 in fluid communication with thevalve chamber 660 when the valve 602 is in the open configuration (FIG.8). The orifice 664 allows fluid from the valve chamber 660 to return tothe reservoir 620 of the hydraulic system 600. In the illustratedconstruction, the hydraulic system 600 includes a secondary valve 668,which will be described in further detail below, disposed between theorifice 664 and the reservoir 620. However, the secondary valve 668 doesnot substantially affect fluid flow from the orifice 664 to thereservoir 620. In other constructions, the secondary valve 668 can beomitted. As the fluid flows from the working volume 616, into the valvechamber 660, and out through the orifice 664, the ram 604 moves towardthe rest position under the biasing force of the return spring 612. Therestrictiveness (i.e., the cross-sectional area) of the orifice 664 canbe selected to provide a desired speed and pressure at which the ram 604returns toward the rest position.

As the ram 604 moves toward the rest position, the pressure of the fluidwithin the working volume 616 is created by the energy stored within thereturn spring 612. Therefore, as the ram 604 continues to move towardthe rest position, energy is released from the return spring 612 causingthe pressure of the fluid in the working volume 616 to drop. Once theram 604 has reached a predetermined position (e.g., the rest or returnedposition in one construction), the pressure within the working volume616 (and therefore the valve chamber 660) falls below the pressurerequired to hold the valve 602 in the open position, against the biasingforce of the spring 656. The tip 652 of the poppet 636 then blocks thepassage 644 of the valve seat, putting the valve 602 in the closedconfiguration (FIG. 7).

The secondary valve 668 includes a plunger 672 having a check ball 676located at a distal end of the plunger 672. The secondary valve 668 alsoincludes an inlet passage 680 in fluid communication with the supplypassage 622, and an outlet passage 684 in fluid communication with thereservoir 620. The inlet passage 680 includes a valve seat 688 shaped toreceive the check ball 676 in order to substantially seal the inletpassage 680 when the secondary valve 668 is in a closed configuration(as illustrated in FIGS. 7 and 8). The plunger 672 is axially moveableto define the closed configuration and an open configuration (not shown)of the valve secondary valve 668. The plunger 672 is biased towards theclosed configuration by a spring 692.

The relative sizes of the poppet 636 and the check ball 676 along withthe relative strengths of the spring 656 and the spring 692 can bealtered to customize the operation of the hydraulic system 600. Severalexamples of possible operation modes are described in detail below.

In a first operation mode of the hydraulic system 600, the valve 602 isconfigured to move from the closed configuration (FIG. 7) to the openconfiguration (FIG. 8) in response to a user input. Once the valve 602is initially opened, the fluid pressure bearing against the face of thepoppet 636 holds the valve 602 in the open configuration, and the fluidfrom the working volume 616 flows through the passage 644, into thevalve chamber 660, and through the orifice 664. The fluid then flowsaround the plunger 672 of the secondary valve 668, through the outletpassage 684, and finally into the reservoir 620. As the fluid flows outof the working volume 616, the return spring 612 pushes the ram 604toward the rest position. When the ram 604 arrives at the rest position,the pressure within the working volume 616 is low enough that the valve602 moves to the closed configuration. Thus, in the first operationmode, the valve 602 is configured to return the ram 604 fully to therest position once actuated by the user.

In the first operation mode, the secondary valve 668 functions as apressure release valve. As such, the check ball 676 only unseats fromthe valve seat 688 if the pressure within the working volume 616 exceedsa predetermined maximum pressure. For example, if the pressure withinthe working volume 616 builds suddenly (e.g., if the ram 604 becomesjammed) and the user does not immediately actuate the valve 602, thepressure acting on the check ball 676 overcomes the biasing force of thespring 692, allowing fluid to flow from the working volume 616 throughthe inlet passage 680, then through the outlet passage 684 and into thereservoir 620. Once the pressure of the working volume 616 falls belowthe predetermined pressure, the spring 692 forces the secondary valve668 closed, reseating the check ball 676 on the valve seat 688.

In a second operation mode of the hydraulic system 600, the secondaryvalve 668 is configured to automatically return the ram 604 toward therest position, without requiring input from the user. When the pressurewithin the working volume 616 reaches a predetermined pressure (e.g.,when the ram 604 reaches the actuated position and/or when the ram 604experiences a predetermined maximum load at any point during the strokeof the ram 604), the pressure acting on the check ball 676 overcomes thebiasing force of the spring 692, allowing fluid to flow from the workingvolume 616 through the inlet passage 680, then through the outletpassage 684 and into the reservoir 620. As the fluid flows out of theworking volume 616, the ram 604 moves toward the rest position, and thepressure within the working volume 616 decreases. The plunger 672 of thesecondary valve 668 can include a face area greater than the area of thecheck ball 676, similar to the relationship between the tip 652 and thepoppet 636 of the valve 602 described previously. Alternatively, thesecond valve 668 can include a pointed tip in place of the check ball676, similar to the tip 652 of the valve 602. Accordingly, once thesecondary valve 668 opens, ram 604 returns toward the rest positionuntil the pressure within the working volume 616 drops to a closingpressure of the valve 668.

In one construction, the secondary valve 668 is configured to move tothe closed configuration at a pressure of the working volume 616corresponding with the ram 604 reaching the rest position. In thisconstruction, the ram 604 is fully returned to the rest position withoutrequiring any input from the user (i.e., the user is not required toactuate the valve 602). In another construction, the secondary valve 668is configured to move to the closed configuration at an intermediateposition of the ram 604 (i.e., prior to the ram 604 reaching the restposition). In this construction, if desired, the ram 604 can be advancedtoward the actuated position (e.g., to perform a work operation) fromthe intermediate position, or the user can actuate the valve 602 toreturn the ram 604 fully to the rest position.

In other constructions, the hydraulic system 600 can include additionalmechanical or electronic control arrangements to provide additionaloperating modes, as may be desired.

Various features of the invention are set forth in the following claims.

What is claimed is:
 1. A valve for selectively fluidly communicating afirst fluid volume and a second fluid volume, the valve comprising: avalve body; an inlet orifice in fluid communication with the first fluidvolume; an outlet aperture in fluid communication with the second fluidvolume; an activation member axially movable relative to the valve body;a first plunger axially movable within the body, the first plungerincluding a central aperture that provides a fluid flow path between thefirst and second fluid volumes; a second plunger including a contactsurface, the second plunger being axially movable relative to the firstplunger between a sealed position in which the contact surface engagesthe central aperture to form a seal with the central aperture thatprevents fluid flow through the central aperture, and an unsealedposition in which the contact surface is spaced from the centralaperture to permit fluid flow through the central aperture; and abiasing member that biases the second plunger toward the sealedposition, wherein the valve is operable in a first mode in which thevalve opens in response to manual actuation of the activation member,and wherein the valve is operable in a second mode in which the valveopens when a pressure difference between the first and second fluidvolumes reaches a predetermined value, and the valve closes when thepressure difference between the first and second fluid volumes is lessthan the predetermined value.
 2. The valve of claim 1, wherein a distalportion of the second plunger forms a seal with the inlet orifice whenthe valve is closed, and wherein the distal portion is spaced from theinlet orifice when the valve is open.
 3. The valve of claim 2, whereinthe first plunger is movable between a first position in which a portionof the first plunger at least partially blocks the outlet aperture toinhibit fluid flow through the outlet aperture and a second position inwhich the outlet aperture is unblocked to permit substantially unimpededfluid flow through the outlet aperture.
 4. The valve of claim 3,wherein, in the first mode, the first plunger is axially movableindependently of the second plunger as the first plunger moves from thefirst position to an intermediate position between the first positionand the second position, and wherein the second plunger is axiallymovable with the first plunger as the first plunger moves from theintermediate position toward the second position.
 5. The valve of claim4, wherein a periphery of the central aperture bears against the contactsurface of the second plunger to move the second plunger with the firstplunger as the first plunger moves from the intermediate position towardthe second position.
 6. The valve of claim 3, wherein the biasing memberthat biases the second plunger is a second biasing member, and whereinthe valve further includes a first biasing member that biases the firstplunger toward the first position.
 7. The valve of claim 1, wherein thefirst plunger is coupled to the activation member for axial movementwith the activation member.
 8. The valve of claim 1, wherein a distalportion of the second plunger forms a seal with the inlet orifice whenthe valve is closed, and wherein the distal portion is spaced from theinlet orifice when the valve is open.
 9. The valve of claim 8, whereinthe distal portion of the second plunger includes a pointed tip.
 10. Thevalve of claim 1, wherein the first plunger includes a hollow,cylindrical portion, and wherein the second plunger is at leastpartially received within the cylindrical portion.
 11. The valve ofclaim 10, wherein the distal portion of the second plunger extendsthrough the central aperture of the first plunger, and wherein a gap isdefined between the distal portion and the central aperture.
 12. Thevalve of claim 11, wherein the gap is a first gap, wherein the secondplunger includes a body disposed within the cylindrical portion of thefirst plunger, and wherein a second gap is defined between the body andthe cylindrical portion.
 13. The valve of claim 1, wherein thepredetermined value is about 7,600 psi.
 14. The valve of claim 1,wherein, in the second mode, the valve closes as soon as the pressuredifference between the first and second fluid volumes drops below thepredetermined value.
 15. The valve of claim 1, wherein, in the firstmode, when the valve is opened in response to manual actuation of theactivation member, the valve remains open until the pressure differencebetween the first and second fluid volumes is substantially zero.
 16. Avalve for selectively fluidly communicating a first fluid volume and asecond fluid volume, the valve comprising: a valve body; an inletorifice in fluid communication with the first fluid volume; an outletaperture in fluid communication with the second fluid volume; anactivation member axially movable relative to the valve body; a firstplunger axially movable within the body, the first plunger including acentral aperture that provides a fluid flow path between the first andsecond fluid volumes; and a second plunger at least partially receivedwithin a hollow cylindrical portion of the first plunger, the secondplunger including a distal portion extending through the centralaperture to define a gap therebetween, the second plunger being axiallymovable relative to the first plunger, wherein the valve is operable ina first mode in which the valve opens in response to manual actuation ofthe activation member, and wherein the valve is operable in a secondmode in which the valve opens when a pressure difference between thefirst and second fluid volumes reaches a predetermined value, and thevalve closes when the pressure difference between the first and secondfluid volumes is less than the predetermined value.
 17. The valve ofclaim 16, wherein the second plunger includes a contact surface, andwherein the second plunger is axially movable relative to the firstplunger between a sealed position in which the contact surface engagesthe central aperture to form a seal with the central aperture thatprevents fluid flow through the central aperture, and an unsealedposition in which the contact surface is spaced from the centralaperture to permit fluid flow through the central aperture.
 18. Thevalve of claim 17, wherein the valve further includes a biasing memberthat biases the second plunger toward the sealed position.
 19. A valvefor selectively fluidly communicating a first fluid volume and a secondfluid volume, the valve comprising: a valve body; an inlet orifice influid communication with the first fluid volume; an outlet aperture influid communication with the second fluid volume; an activation memberaxially movable relative to the valve body; a first plunger axiallymovable within the body between a first position in which a portion ofthe first plunger at least partially blocks the outlet aperture toinhibit fluid from flowing between the first and second fluid volumesthrough the outlet aperture and a second position in which the outletaperture is unblocked to permit substantially unimpeded fluid flowbetween the first and second fluid volumes through the outlet aperture,the first plunger including a central aperture that provides a fluidflow path between the first and second fluid volumes; and a secondplunger including a contact surface, the second plunger being axiallymovable relative to the first plunger between a sealed position in whichthe contact surface engages the central aperture to form a seal with thecentral aperture and prevent fluid flow through the central aperture,and an unsealed position in which the contact surface is spaced from thecentral aperture to permit fluid flow through the central aperture,wherein the valve is operable in a first mode in which the valve opensin response to manual actuation of the activation member, wherein thevalve is operable in a second mode in which the valve opens when apressure difference between the first and second fluid volumes reaches apredetermined value, and the valve closes when the pressure differencebetween the first and second fluid volumes is less than thepredetermined value, wherein, in the first mode, the first plunger isaxially movable independently of the second plunger member as the firstplunger moves from the first position to an intermediate positionbetween the first position and the second position, and wherein thesecond plunger is axially movable with the first plunger as the firstplunger moves from the intermediate position toward the second position.